Bump sphinx-rtd-theme from 0.1.9 to 2.0.0 in /docs

Bumps [sphinx-rtd-theme](https://github.com/readthedocs/sphinx_rtd_theme) from 0.1.9 to 2.0.0.
- [Changelog](https://github.com/readthedocs/sphinx_rtd_theme/blob/master/docs/changelog.rst)
- [Commits](readthedocs/sphinx_rtd_theme@0.1.9...2.0.0)

---
updated-dependencies:
- dependency-name: sphinx-rtd-theme
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/requirements.txt

@@ -13,7 +13,7 @@ requests==2.32.3
 six==1.11.0
 snowballstemmer==1.2.1
 Sphinx==1.5.1
-sphinx-rtd-theme==0.1.9
+sphinx-rtd-theme==2.0.0
 sphinxcontrib-phpdomain==0.12.0
 urllib3==2.2.3
 cakephp-theme